Turbulent Mass Transfer Model For The Simulation Of Liquid-Solid Cfb Risers And Its Verification

Rigorous simulation of mass transfer process in liquid-solid circulating fluidized bed (LSCFB) system is challenging not only due to the fluidization but also due to the existing turbulence. In this paper, the recently developed (c(2)) over bar-epsilon(c) approach is introduced to characterize the turbulent mass diffusion in LSCFB riser so that the empirical turbulent mass diffusivity are abandoned. As for describing the liquid-solid turbulent flow, the k(l) - epsilon(l) - k(s) - epsilon(s) - theta formulations are adopted. With the proposed model, the distributions of species concentration and phase velocity as well as solids holdup can be predicted simultaneously. In this paper the integrated model is established and simulations are conducted for a riser involving an impulse tracer test process so that the proposed model can be validated. The turbulent Schmidt number is found to be varied but not a constant throughout the riser, which reveals that the use of constant turbulent Schmidt number for the traditional model is questionable. (C) 2020 Elsevier B.V. All rights reserved.